Positive resist composition and patterning process

ABSTRACT

A positive resist composition is provided comprising (A) an acid generator in the form of a sulfonium salt consisting of a fluorine-containing sulfonate anion and a fluorine-containing sulfonium cation, (B) a quencher in the form of a sulfonium salt containing at least two fluorine atoms in its cation or containing at least 5 fluorine atoms in its anion and cation, and (C) a base polymer comprising repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and/or repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group. The resist composition exhibits a high sensitivity, high resolution and improved LWR or CDU.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2020-166646 filed in Japan on Oct. 1, 2020, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a positive resist composition and a pattern forming process.

BACKGROUND ART

To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. In particular, the enlargement of the logic memory market to comply with the wide-spread use of smart phones drives forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 10-nm node by double patterning of the ArF immersion lithography has been implemented in a mass scale. Manufacturing of 7-nm node devices as the next generation by the double patterning technology is approaching to the verge of high-volume application. The candidate for 5-nm node devices as the next generation but one is EUV lithography.

The EUV lithography enables to form small size patterns because the wavelength (13.5 nm) of EUV is as short as 1/14.3 of the wavelength (193 nm) of ArF excimer laser light. However, since the number of photons available from EUV exposure is accordingly 1/14.3 of that from ArF excimer laser exposure, there arises the problem of shot noise that a variation in number of photons causes an increase in edge roughness (LER or LWR) and a lowering of CDU (Non-Patent Document 1).

In addition to the variations due to shot noise, it is pointed out in Non-Patent Document 2 that the uneven distribution of acid generator and quencher components in a resist film causes a variation in feature size. In the EUV lithography for forming very small size patterns, there exists a need for a resist material of uniform distribution system.

CITATION LIST

-   Non-Patent Document 1: SPIE Vol. 3331, p531 (1998) -   Non-Patent Document 2: SPIE Vol. 9776, p97760V-1 (2016)

DISCLOSURE OF INVENTION

An object of the invention is to provide a positive tone resist composition which exhibits a higher sensitivity and resolution than prior art positive resist compositions, and forms a pattern of good profile with a reduced LWR or improved CDU after exposure; and a pattern forming process using the same.

The inventors presumed that for obtaining a positive tone resist composition having a high sensitivity, high resolution, reduced LWR and improved CDU as desired in the recent market, it is necessary to prevent resist material components such as acid generator and quencher from agglomerating together and to disperse or distribute them uniformly. It is believed effective for this purpose to utilize the electrical repulsion force of fluorine atoms to prevent the relevant components from agglomeration. The inventors have found that when a sulfonium salt consisting of a sulfonate anion and a sulfonium cation which both contain at least one fluorine atom is added as the acid generator, and a sulfonium salt consisting of an anion and a cation, the cation containing at least two fluorine atoms or the anion and cation containing at least 5 fluorine atoms in total, is added as the quencher, there is formulated a resist composition in which the acid generator and the quencher are uniformly distributed because of their mutual repulsion.

In one aspect, the invention provides a positive resist composition comprising:

(A) an acid generator in the form of a sulfonium salt consisting of a sulfonate anion having at least one fluorine atom and a sulfonium cation having at least one fluorine atom,

(B) a quencher in the form of a sulfonium salt consisting of a cation and an anion, the cation containing at least two fluorine atoms or the anion and cation containing at least 5 fluorine atoms in total, and

(C) a base polymer comprising repeat units of at least one type selected from repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group.

In a preferred embodiment, the quencher (B) is a sulfonium salt in which the cation contains at least 3 fluorine atoms or the anion and cation contain at least 6 fluorine atoms in total.

In a preferred embodiment, the sulfonate anion in the acid generator (A) further contains an iodine atom.

In a preferred embodiment, the sulfonate anion in the acid generator (A) has the formula (1-1) or (1-2).

Herein R¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine. R² is a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine.

In a preferred embodiment, the sulfonate anion has the formula (1-3).

Herein p is an integer of 1 to 3, q is an integer of 1 to 5, r is an integer of 0 to 3, and q+r is from 1 to 5. L¹ is a single bond, ether bond, ester bond, amide bond, imide bond or a C₁-C₆ saturated hydrocarbylene group in which any constituent —CH₂— may be replaced by an ether bond or ester bond. L² is a single bond or C₁-C₂₀ hydrocarbylene group which may contain a heteroatom in case of p=1, and a C₁-C₂₀ (p+1)-valent hydrocarbon group which may contain a heteroatom in case of p=2 or 3. L³ is a single bond, ether bond or ester bond. Rf¹ to Rf⁴ are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf¹ to Rf⁴ being fluorine or trifluoromethyl, and Rf¹ and Rf², taken together, may form a carbonyl group. R³ is a hydroxy group, carboxy group, fluorine, chlorine, bromine, or amino group, or a C₁-C₂₀ hydrocarbyl group, C₁-C₂₀ hydrocarbyloxy group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbylcarbonyloxy group, or C₁-C₂₀ hydrocarbylsulfonyloxy group, which may contain fluorine, chlorine, bromine, hydroxy, amino or ether bond, or —N(R^(3A))(R^(3B)), —N(R^(3C))—C(═O)—R^(3D) or —N(R^(3C))—C(═O)—O—R^(3D). R^(3A) and R^(3B) are each independently hydrogen or a C₁-C₆ saturated hydrocarbyl group, R^(3C) is hydrogen or a C₁-C₆ saturated hydrocarbyl group, in which some or all hydrogen may be substituted by a halogen, hydroxy moiety, C₁-C₆ saturated hydrocarbyloxy moiety, C₂-C₆ saturated hydrocarbylcarbonyl moiety, or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety, and R^(3D) is a C₁-C₁₆ aliphatic hydrocarbyl group, C₆-C₁₂ aryl group or C₇-C₁₅ aralkyl group, in which some or all hydrogen may be substituted by a halogen, hydroxy moiety, C₁-C₆ saturated hydrocarbyloxy moiety, C₂-C₆ saturated hydrocarbylcarbonyl moiety, or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety.

In a preferred embodiment, the anion of the sulfonium salt as quencher (B) is a carboxylate, sulfonamide, alkoxide or non-α-fluorinated sulfonate anion.

More preferably, the carboxylate anion has the formula (2-1), the sulfonamide anion has the formula (2-2), the alkoxide anion has the formula (2-3), and the non-α-fluorinated sulfonate anion has the formula (2-4).

Herein R¹¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine and/or a heteroatom exclusive of fluorine. R¹² is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine and/or a heteroatom exclusive of fluorine. R¹³ is hydrogen or a C₁-C₂₀ hydrocarbyl group which may contain a heteroatom. R¹⁴ is a C₁-C₈ saturated hydrocarbyl group having at least two fluorine atoms or a C₆-C₁₀ aryl group having at least two fluorine atoms. R¹⁵ is a C₁-C₁₂ aliphatic hydrocarbyl group or C₆-C₁₀ aryl group, any constituent —CH₂— in the aliphatic hydrocarbyl group may be replaced by —N(H)—, ether bond, or ester bond, some or all of the hydrogen atoms in the aliphatic hydrocarbyl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₆-C₁₀ aryl moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, some or all of the hydrogen atoms in the aryl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, with the proviso that R¹⁵ has no fluorine on the α-carbon relative to the sulfo group.

In the sulfonium salt (A), the sulfonium cation having at least one fluorine atom preferably has the formula (3).

Herein R^(a1) is a C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one atom selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine. R^(a2) and R^(a3) are each independently a C₁-C₂₀ hydrocarbyl group or C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one atom selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine. R^(a1) and R^(a2), or R^(a2) and R^(a3) may bond together to form a ring with the sulfur atom to which they are attached.

In a preferred embodiment, the repeat unit (a1) has the formula (a1) and the repeat unit (a2) has the formula (a2).

Herein R^(A) is each independently hydrogen or methyl. X¹ is a single bond, phenylene group, naphthylene group, or a C₁-C₁₂ linking group containing at least one moiety selected from an ether bond, ester bond and lactone ring. X² is a single bond, ester bond or amide bond. X³ is a single bond, ether bond or ester bond. R²¹ and R²² are each independently an acid labile group. R²³ is fluorine, trifluoromethyl, cyano or a C₁-C₆ saturated hydrocarbyl group. R²⁴ is a single bond or a C₁-C₆ alkanediyl group in which some carbon may be replaced by an ether bond or ester bond; a is 1 or 2, b is an integer of 0 to 4, and 1≤a+b≤5.

In a preferred embodiment, the base polymer further comprises repeat units containing an adhesive group selected from among hydroxy, carboxy, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether bond, ester bond, sulfonic ester bond, cyano, amide bond, —O—C(═O)—S—, and —O—C(═O)—NH—.

The resist composition may further comprise (D) an organic solvent and/or (E) a surfactant.

In another aspect, the invention provides a pattern forming process comprising the steps of applying the positive resist composition defined above to form a resist film on a substrate, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer.

The high-energy radiation is typically i-line, KrF excimer laser, ArF excimer laser, EB, or EUV of wavelength 3 to 15 nm.

In a further aspect, the invention provides a sulfonium salt having the formula (1-3-1):

wherein R⁴ is a single bond or C₁-C₆ alkanediyl group, R⁵ is hydrogen or trifluoromethyl, and X is hydroxy or iodine.

Advantageous Effects of Invention

The positive resist composition of the invention forms a resist film having a high sensitivity and reduced LWR or improved CDU because the acid generator and the quencher are uniformly distributed in the resist film. By virtue of these advantages, the resist composition is fully useful in commercial application and suited as a micropatterning material for the fabrication of VLSIs, micropatterning material for the fabrication of photomasks by EB writing, and micropatterning material adapted for EB or EUV lithography. The resist composition may be used not only in the lithography for forming semiconductor circuits, but also in the formation of mask circuit patterns, micromachines, and thin-film magnetic head circuits.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. The notation (C_(n)-C_(m)) means a group containing from n to m carbon atoms per group. The term “group” and “moiety” are interchangeable. The fluorine-containing compound is also referred to as fluorinated compound. In chemical formulae, the broken line designates a valence bond, and Me stands for methyl and Ac for acetyl.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

LWR: line width roughness

CDU: critical dimension uniformity

Positive Resist Composition

The positive resist composition of the invention is defined as comprising (A) an acid generator in the form of a sulfonium salt consisting of a sulfonate anion having at least one fluorine atom and a sulfonium cation having at least one fluorine atom, (B) a quencher in the form of a sulfonium salt consisting of a cation and an anion, the cation containing at least two fluorine atoms or the anion and cation containing at least 5 fluorine atoms in total, and (C) a base polymer comprising repeat units of at least one type selected from repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group. Since the sulfonium salt as component (A) or acid generator contains fluorine in both the cation and the anion, and the sulfonium salt as component (B) or quencher contains at least 2 fluorine atoms in its cation or totally at least 5 fluorine atoms in its anion and cation, their molecules do not agglomerate together due to the electric repulsion of negatively charged fluorine atoms, and are uniformly distributed. As a consequence, the resist pattern after development is improved in LWR and CDU.

In the acid generator (A), preferably the sulfonate anion further contains iodine. Since iodine is highly absorptive to EUV, the number of photons available upon exposure is increased, and the physical contrast is improved. There is obtained a resist composition having a higher sensitivity and contrast.

(A) Acid Generator

Component (A) is an acid generator which is a sulfonium salt consisting of a sulfonate anion having at least one fluorine atom (referred to as fluorinated sulfonate anion, hereinafter) and a sulfonium cation having at least one fluorine atom (referred to as fluorinated sulfonium cation, hereinafter).

Typically, the fluorinated sulfonate anion has the formula (1-1) or (1-2).

In formula (1-1), R¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine. The C₁-C₄₀ hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof are the same as will be exemplified below for the hydrocarbyl group R^(1a) in formula (1-1-1).

Of the anions having formula (1-1), anions having the formula (1-1-1) are preferred.

Herein, R^(HF) is hydrogen or trifluoromethyl, preferably trifluoromethyl. R^(1a) is a C₁-C₃₈ hydrocarbyl group which may contain a heteroatom. Suitable heteroatoms include oxygen, nitrogen, sulfur and halogen, with oxygen being preferred. Of the hydrocarbyl groups, those of 6 to 30 carbon atoms are preferred because a high resolution is available in fine pattern formation.

The hydrocarbyl group R^(1a) may be saturated or unsaturated and straight, branched or cyclic. Suitable hydrocarbyl groups include C₁-C₃₈ alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, icosanyl; C₃-C₃₈ cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl, tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl, dicyclohexylmethyl; C₂-C₃₈ unsaturated hydrocarbyl groups such as allyl, 3-cyclohexenyl, tetracyclododecenyl; C₆-C₃₈ aryl groups such as phenyl, 1-naphthyl, 2-naphthyl; C₇-C₃₈ aralkyl groups such as benzyl and diphenylmethyl; C₂₀-C₃₈ hydrocarbyl groups of steroid skeleton which may contain a heteroatom; and combinations thereof.

In these groups, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or some carbon may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, cyano, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate, lactone ring, sultone ring, carboxylic anhydride or haloalkyl moiety. Examples of the heteroatom-containing hydrocarbyl group include tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl, acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl, 2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and 3-oxocyclohexyl.

Examples of the anion having formula (1-1) are shown below, but not limited thereto.

In formula (1-2), R² is a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof are as exemplified above for the hydrocarbyl group R^(1a) in formula (1-1-1).

Examples of the anion having formula (1-2) are shown below, but not limited thereto.

In the embodiment wherein the sulfonate anion further contains iodine, a sulfonate anion having the formula (1-3) is preferred.

In formula (1-3), p is an integer of 1 to 3; q is an integer of 1 to 5, r is an integer of 0 to 3, and 1≤q+r≤5.

In formula (1-3), L¹ is a single bond, ether bond, ester bond, amide bond, imide bond, or a C₁-C₆ saturated hydrocarbylene group in which any constituent —CH₂— may be replaced by an ether bond or ester bond. Notably, the constituent —CH₂— may be positioned at the end of the saturated hydrocarbylene group.

The C₁-C₆ saturated hydrocarbylene group L may be straight, branched or cyclic. Examples thereof include C₁-C₆ alkanediyl groups such as methanediyl, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, and hexane-1,6-diyl; C₃-C₆ cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof.

In formula (1-3), L² is a single bond or a C₁-C₂₀ hydrocarbylene group which may contain a heteroatom in case of p=1; and a C₁-C₂₀ (p+1)-valent hydrocarbon group which may contain a heteroatom in case of p=2 or 3.

The C₁-C₂₀ hydrocarbylene group L² may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkanediyl groups such as methanediyl, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, and dodecane-1,12-diyl; C₃-C₂₀ cyclic saturated hydrocarbylene groups such as cyclopentanediyl, cyclohexanediyl, norbornanediyl and adamantanediyl; C₂-C₂₀ unsaturated aliphatic hydrocarbylene groups such as vinylene and propene-1,3-diyl; C₆-C₂₀ arylene groups such as phenylene and naphthylene; and combinations thereof. The C₁-C₂₀ (p+1)-valent hydrocarbon group L² may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include groups obtained by removing one or two hydrogen atoms from the above-described examples of the C₁-C₂₀ hydrocarbylene group.

In formula (1-3), L³ is a single bond, ether bond or ester bond.

In formula (1-3), R³ is a hydroxy group, carboxy group, fluorine, chlorine, bromine or amino group, or a C₁-C₂₀ hydrocarbyl group, C₁-C₂₀ hydrocarbyloxy group, C₂-C₂₀ hydrocarbylcarbonyl group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbylcarbonyloxy group or C₁-C₂₀ hydrocarbylsulfonyloxy group, which may contain fluorine, chlorine, bromine, hydroxy, amino or ether bond,

or —N(R^(3A))(R^(3B)), —N(R^(3C))—C(═O)—R^(3D) or —N(R^(3C))—C(═O)O—R^(3D). R^(3A) and R^(3B) are each independently hydrogen or a C₁-C₆ saturated hydrocarbyl group. R^(3C) is hydrogen or a C₁-C₆ saturated hydrocarbyl group in which some or all of the hydrogen atoms may be substituted by halogen, hydroxy, C₁-C₆ saturated hydrocarbyloxy, C₂-C₆ saturated hydrocarbylcarbonyl or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety. R^(3D) is a C₁-C₁₆ aliphatic hydrocarbyl group, C₆-C₁₂ aryl group or C₇-C₁₅ aralkyl group, in which some or all of the hydrogen atoms may be substituted by halogen, hydroxy, C₁-C₆ saturated hydrocarbyloxy, C₂-C₆ saturated hydrocarbylcarbonyl or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety. When p and/or r is 2 or more, groups R³ may be the same or different.

The C₁-C₂₀ hydrocarbyl group, and hydrocarbyl moiety in the C₁-C₂₀ hydrocarbyloxy group, C₂-C₂₀ hydrocarbylcarbonyl group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbylcarbonyloxy group or C₁-C₂₀ hydrocarbylsulfonyloxy group, represented by R³, may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, heptadecyl, octadecyl, nonadecyl and icosyl; C₃-C₂₀ cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, adamantyl; C₂-C₂₀ alkenyl groups such as vinyl, propenyl, butenyl and hexenyl; C₂-C₂₀ cyclic unsaturated aliphatic hydrocarbyl groups such as cyclohexenyl and norbornenyl; C₂-C₂₀ alkynyl groups such as ethynyl, propynyl and butynyl; C₆-C₂₀ aryl groups such as phenyl, methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, sec-butylphenyl, tert-butylphenyl, naphthyl, methylnaphthyl, ethylnaphthyl, n-propylnaphthyl, isopropylnaphthyl, n-butylnaphthyl, isobutylnaphthyl, sec-butylnaphthyl, tert-butylnaphthyl; C₇-C₂₀ aralkyl groups such as benzyl and phenethyl; and combinations thereof.

The C₁-C₆ saturated hydrocarbyl groups represented by R^(3A), R^(3B) and R^(3C) may be straight, branched or cyclic. Examples thereof include C₁-C₆ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl and n-hexyl; and C₃-C₆ cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. Examples of the saturated hydrocarbyl moiety in the C₁-C₆ saturated hydrocarbyloxy group represented by R^(3C) are as exemplified above for the saturated hydrocarbyl group. Examples of the saturated hydrocarbyl moiety in the C₂-C₆ saturated hydrocarbylcarbonyl group and C₂-C₆ saturated hydrocarbylcarbonyloxy group represented by R^(3C) are as exemplified above for the C₁-C₆ saturated hydrocarbyl group, but of 1 to 5 carbon atoms.

The aliphatic hydrocarbyl group represented by R^(3D) may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₁₆ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl, and pentadecyl; C₃-C₁₆ cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, adamantyl; C₂-C₁₆ alkenyl groups such as vinyl, propenyl, butenyl and hexenyl; C₂-C₁₆ alkynyl groups such as ethynyl, propynyl and butynyl; C₃-C₁₆ cyclic unsaturated aliphatic hydrocarbyl groups such as cyclohexenyl and norbornenyl; and combinations thereof. Examples of the C₆-C₁₂ aryl group R^(3D) include phenyl and naphthyl. Examples of the C₇-C₁₅ aralkyl group R^(3D) include benzyl and phenethyl. Of the groups represented by R^(3D), examples of the hydrocarbyl moiety in the C₁-C₆ saturated hydrocarbyloxy group are as exemplified above for the C₁-C₆ saturated hydrocarbyl group represented by R^(3A), R^(3B) and R^(3C); examples of the hydrocarbyl moiety in the C₂-C₆ saturated hydrocarbylcarbonyl group or C₂-C₆ saturated hydrocarbylcarbonyloxy group are as exemplified above for the C₁-C₆ saturated hydrocarbyl group, but of 1 to 5 carbon atoms.

In formula (1-3), Rf¹ to Rf⁴ are each independently hydrogen, fluorine or trifluoromethyl, at least one thereof being fluorine or trifluoromethyl. Also Rf¹ and Rf², taken together, may form a carbonyl group. The total number of fluorine atoms in Rf¹ to Rf⁴ is preferably at least 2, more preferably at least 3.

Examples of the anion having formula (1-3) are shown below, but not limited thereto.

The fluorinated sulfonium cation preferably has the formula (3).

In formula (3), R^(a1) is a C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one element selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine. R^(a2) and R^(a3) are each independently a C₁-C₂₀ hydrocarbyl group or C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one element selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine.

The total number of fluorine atoms in R^(a1), R^(a2) and R^(a3) is preferably at least 2, more preferably at least 3.

The C₁-C₂₀ hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, heptadecyl, octadecyl, nonadecyl and icosyl; C₃-C₂₀ cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, adamantyl; C₂-C₂₀ alkenyl groups such as vinyl, propenyl, butenyl and hexenyl; C₂-C₂₀ alkynyl groups such as ethynyl, propynyl and butynyl; C₃-C₂₀ cyclic unsaturated aliphatic hydrocarbyl groups such as cyclohexenyl and norbornenyl; C₆-C₂₀ aryl groups such as phenyl, methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, sec-butylphenyl, tert-butylphenyl, naphthyl, methylnaphthyl, ethylnaphthyl, n-propylnaphthyl, isopropylnaphthyl, n-butylnaphthyl, isobutylnaphthyl, sec-butylnaphthyl, tert-butylnaphthyl; C₇-C₂₀ aralkyl groups such as benzyl and phenethyl; and combinations thereof.

In the C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen, or halogen exclusive of fluorine, and some carbon may be replaced by a moiety containing a heteroatom such as oxygen, sulfur, or nitrogen, so that the group may contain a hydroxy moiety, chlorine, bromine, iodine, cyano moiety, nitro moiety, carbonyl moiety, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride or haloalkyl moiety.

A pair of R^(a1) and R^(a2), or R^(a2) and R^(a3) may bond together to form a ring with the sulfur atom to which they are attached. In this case, rings of the following structure are preferred.

Examples of the sulfonium cation having formula (3) are shown below, but not limited thereto.

Of the sulfonium salts containing an anion of formula (1-3), preferred are those sulfonium salts having the formula (1-3-1):

wherein R⁴ is a single bond or a C₁-C₆ alkanediyl group, R⁵ is hydrogen or trifluoromethyl, and X is a hydroxy group or iodine.

In the positive resist composition, the acid generator (A) is preferably present in an amount of 0.1 to 100 parts by weight, more preferably 1 to 50 parts by weight per 100 parts by weight of the base polymer (C) to be described later.

(B) Quencher

Component (B) is a quencher which is a sulfonium salt consisting of a cation and an anion, the cation containing at least two fluorine atoms or the anion and cation containing at least 5 fluorine atoms in total. The preferred anion is a carboxylate, sulfonamide, alkoxide or non-α-fluorinated sulfonate anion.

Preferably, the carboxylate anion has the formula (2-1), the sulfonamide anion has the formula (2-2), the alkoxide anion has the formula (2-3), and the non-α-fluorinated sulfonate anion has the formula (2-4).

In formula (2-1), R¹¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine and/or a heteroatom exclusive of fluorine.

In formula (2-2), R¹² is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine and/or a heteroatom exclusive of fluorine. R¹³ is hydrogen or a C₁-C₂₀ hydrocarbyl group which may contain a heteroatom.

In formula (2-3), R¹⁴ is a C₁-C₈ saturated hydrocarbyl group having at least two fluorine atoms or a C₆-C₁₀ aryl group having at least two fluorine atoms.

In formula (2-4), R⁵ is a C₁-C₁₂ aliphatic hydrocarbyl group or C₆-C₁₀ aryl group. Any constituent —CH₂— in the aliphatic hydrocarbyl group may be replaced by —N(H)—, ether bond or ester bond, some or all of the hydrogen atoms in the aliphatic hydrocarbyl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₆-C₁₀ aryl moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, some or all of the hydrogen atoms in the aryl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, with the proviso that R⁵ has no fluorine at the α-position relative to the sulfo group.

The C₁-C₄₀ hydrocarbyl group represented by R¹¹ and R¹² may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₄₀ alkyl groups, C₃-C₄₀ cyclic saturated hydrocarbyl groups, C₂-C₄₀ alkenyl groups, C₂-C₄₀ alkynyl groups, C₃-C₃₀ cyclic unsaturated aliphatic hydrocarbyl groups, C₆-C₄₀ aryl groups, C₇-C₄₀ aralkyl groups, and combinations thereof. In these groups, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen, fluorine or halogen exclusive of fluorine, and some carbon may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain an ester bond, ether bond, thioether bond, carbonyl moiety, sulfonyl moiety, carbonate moiety, carbamate moiety, sulfone moiety, amino moiety, amide bond, hydroxy moiety, thiol moiety, nitro moiety, fluorine, chlorine, bromine, iodine or the like.

The C₁-C₂₀ hydrocarbyl group represented by R¹³ may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkyl groups, C₃-C₂₀ cyclic saturated hydrocarbyl groups, C₂-C₂₀ alkenyl groups, C₂-C₂₀ alkynyl groups, C₃-C₂₀ cyclic unsaturated aliphatic hydrocarbyl groups, C₆-C₂₀ aryl groups, C₇-C₂₀ aralkyl groups, and combinations thereof. In these groups, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some carbon may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain an ester bond, ether bond, thioether bond, carbonyl moiety, sulfonyl moiety, carbonate moiety, carbamate moiety, sulfone moiety, amino moiety, amide bond, hydroxy moiety, thiol moiety, nitro moiety, fluorine, chlorine, bromine, iodine or the like.

The C₁-C₈ saturated hydrocarbyl group having at least two fluorine atoms, represented by R¹⁴, may be straight, branched or cyclic. Examples thereof include C₁-C₈ alkyl groups, C₃-C₈ cyclic saturated hydrocarbyl groups, and combinations thereof, in which at least 2 hydrogen atoms are substituted by fluorine atoms.

The C₁-C₁₂ aliphatic hydrocarbyl group R¹¹ may be straight, branched or cyclic. Examples thereof include C₁-C₁₂ alkyl groups, C₃-C₁₂ cyclic saturated hydrocarbyl groups, C₂-C₁₂ alkenyl groups, C₂-C₁₂ alkynyl groups, C₃-C₁₂ cyclic unsaturated aliphatic hydrocarbyl groups, and combinations thereof.

Examples of the carboxylate anion are shown below, but not limited thereto.

Examples of the sulfonamide anion are shown below, but not limited thereto.

Examples of the alkoxide anion are shown below, but not limited thereto.

Examples of the non-α-fluorinated sulfonate anion are shown below, but not limited thereto.

The sulfonium cation in the quencher (B) may or may not contain fluorine. Fluorine-containing sulfonium cations having formula (3) are preferred.

The preferred quencher (B) is a sulfonium salt in which the cation contains at least 3 fluorine atoms or the anion and cation contain at least 6 fluorine atoms in total.

In the positive resist composition, the quencher (B) is preferably present in an amount of 0.01 to 30 parts by weight, more preferably 0.02 to 20 parts by weight per 100 parts by weight of the base polymer (C) to be described later.

(C) Base Polymer

Component (C) is a base polymer comprising repeat units of at least one type selected from repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group.

In a preferred embodiment, the repeat unit (a1) has the formula (a1) and the repeat unit (a2) has the formula (a2).

In formulae (a1) and (a2), R^(A) is each independently hydrogen or methyl. X¹ is a single bond, phenylene group, naphthylene group, or a C₁-C₁₂ linking group containing at least one moiety selected from an ether bond, ester bond and lactone ring. X² is a single bond, ester bond or amide bond. X³ is a single bond, ether bond or ester bond. R²¹ and R²² are each independently an acid labile group. R²³ is fluorine, trifluoromethyl, cyano or a C₁-C₆ saturated hydrocarbyl group. R²⁴ is a single bond or a C₁-C₆ alkanediyl group in which some carbon may be replaced by an ether bond or ester bond. The subscript “a” is 1 or 2, b is an integer of 0 to 4, and 1≤a+b≤5.

Examples of the monomer from which repeat units (a1) are derived are shown below, but not limited thereto. Herein R^(A) and R²¹ are as defined above.

Examples of the monomer from which repeat units (a2) are derived are shown below, but not limited thereto. Herein R^(A) and R²² are as defined above.

The acid labile groups represented by R²¹ and R²² may be selected from a variety of such groups, for example, those groups having the following formulae (AL-1) to (AL-3).

In formulae (AL-1), c is an integer of 0 to 6. R^(L1) is a C₄-C₄₀, preferably C₄-C₁₅ tertiary hydrocarbyl group, a trihydrocarbylsilyl group in which each hydrocarbyl moiety is a C₁-C₆ saturated hydrocarbyl moiety, a C₄-C₂₀ saturated hydrocarbyl group containing a carbonyl moiety, ether bond or ester bond, or a group having formula (AL-3).

The tertiary hydrocarbyl group RY may be saturated or unsaturated and branched or cyclic. Examples thereof include tert-butyl, tert-pentyl, 1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and 2-methyl-2-adamantyl. Suitable trihydrocarbylsilyl groups include trimethylsilyl, triethylsilyl, and dimethyl-tert-butylsilyl. The saturated hydrocarbyl group containing a carbonyl moiety, ether bond or ester bond may be straight, branched or cyclic, preferably cyclic, and examples thereof include 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, 5-methyl-2-oxooxolan-5-yl, 2-tetrahydropyranyl, and 2-tetrahydrofuranyl.

Examples of the acid labile group having formula (AL-1) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-pentyloxycarbonyl, tert-pentyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl, 1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl, and 2-tetrahydrofuranyloxycarbonylmethyl.

Other examples of the acid labile group having formula (AL-1) include groups having the formulae (AL-1)-1 to (AL-1)-10.

In formulae (AL-1)-1 to (AL-1)-10, c is as defined above. R^(L8) is each independently a C₁-C₁₀ saturated hydrocarbyl group or C₆-C₂₀ aryl group. R^(L9) is hydrogen or a C₁-C₁₀ saturated hydrocarbyl group. R^(L10) is a C₂-C₁₀ saturated hydrocarbyl group or C₆-C₂₀ aryl group. The saturated hydrocarbyl group may be straight, branched or cyclic.

In formula (AL-2), R^(L2) and R^(L3) are each independently hydrogen or a C₁-C₁₈, preferably C₁-C₁₀ saturated hydrocarbyl group. The saturated hydrocarbyl group may be straight, branched or cyclic and examples thereof include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl and n-octyl.

In formula (AL-2), R^(L4) is a C₁-C₁₈, preferably C₁-C₁₀ hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic and typical examples thereof include C₁-C₁₈ saturated hydrocarbyl groups, in which some hydrogen may be substituted by hydroxy, alkoxy, oxo, amino or alkylamino. Examples of the substituted saturated hydrocarbyl group are shown below.

A pair of R^(L2) and R^(L3), R^(L2) and R^(L4), or R^(L3) and R^(L4) may bond together to form a ring with the carbon atom or carbon and oxygen atoms to which they are attached. R^(L2) and R^(L3), R^(L2) and R^(L4), and R^(L3) and R^(L4) taken together to form a ring are each independently a C₁-C₁₈, preferably C₁-C₁₀ alkanediyl group. The ring thus formed is preferably of 3 to 10, more preferably 4 to 10 carbon atoms.

Of the acid labile groups having formula (AL-2), suitable straight or branched groups include those having formulae (AL-2)-1 to (AL-2)-69, but are not limited thereto.

Of the acid labile groups having formula (AL-2), suitable cyclic groups include tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Also included are acid labile groups having the following formulae (AL-2a) and (AL-2b). The base polymer may be crosslinked within the molecule or between molecules with these acid labile groups.

In formulae (AL-2a) and (AL-2b), R^(L11) and R^(L12) are each independently hydrogen or a C₁-C₈ saturated hydrocarbyl group which may be straight, branched or cyclic. Also, R^(L11) and R^(L12) may bond together to form a ring with the carbon atom to which they are attached, and in this case, R^(L11) and R^(L12) are each independently a C₁-C₈ alkanediyl group. R^(L13) is each independently a C₁-C₁₀ saturated hydrocarbylene group which may be straight, branched or cyclic. The subscripts d and e are each independently an integer of 0 to 10, preferably 0 to 5, and f is an integer of 1 to 7, preferably 1 to 3.

In formulae (AL-2a) and (AL-2b), L^(A) is a (f+1)-valent C₁-C₅₀ aliphatic saturated hydrocarbon group, (f+1)-valent C₃-C₅₀ alicyclic saturated hydrocarbon group, (f+1)-valent C₆-C₅₀ aromatic hydrocarbon group or (f+1)-valent C₃-C₅₀ heterocyclic group. In these groups, some carbon may be replaced by a heteroatom-containing moiety, or some carbon-bonded hydrogen may be substituted by a hydroxy, carboxy, acyl moiety or fluorine. L^(A) is preferably a C₁-C₂₀ saturated hydrocarbon group such as saturated hydrocarbylene, trivalent saturated hydrocarbon or tetravalent saturated hydrocarbon group, or C₆-C₃₀ arylene group. The saturated hydrocarbon group may be straight, branched or cyclic. L^(B) is —C(═O)—O—, —NH—C(═O)—O— or —NH—C(═O)—NH—.

Examples of the crosslinking acetal groups having formulae (AL-2a) and (AL-2b) include groups having the formulae (AL-2)-70 to (AL-2)-77.

In formula (AL-3), R^(L5), R^(L6) and R^(L7) are each independently a C₁-C₂₀ hydrocarbyl group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkyl groups, C₃-C₂₀ cyclic saturated hydrocarbyl groups, C₂-C₂₀ alkenyl groups, C₃-C₂₀ cyclic unsaturated aliphatic hydrocarbyl groups, and C₆-C₁₀ aryl groups. A pair of R^(L5) and R^(L6), R^(L5) and R^(L7), or R^(L6) and R^(L7) may bond together to form a C₃-C₂₀ aliphatic ring with the carbon atom to which they are attached.

Examples of the group having formula (AL-3) include tert-butyl, 1,1-diethylpropyl, 1-ethylnorbornyl, 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-isopropylcyclopentyl, 1-methylcyclohexyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, and tert-pentyl.

Examples of the group having formula (AL-3) also include groups having the formulae (AL-3)-1 to (AL-3)-19.

In formulae (AL-3)-1 to (AL-3)-19, R^(L14) is each independently a C₁-C₈ saturated hydrocarbyl group or C₆-C₂₀ aryl group. R^(L15) and R^(L17) are each independently hydrogen or a C₁-C₂₀ saturated hydrocarbyl group. R^(L16) is a C₆-C₂₀ aryl group. The saturated hydrocarbyl group may be straight, branched or cyclic. Typical of the aryl group is phenyl. R^(F) is fluorine or trifluoromethyl, and g is an integer of 1 to 5.

Other examples of the group having formula (AL-3) include groups having the formulae (AL-3)-20 and (AL-3)-21. The base polymer may be crosslinked within the molecule or between molecules with these acid labile groups.

In formulae (AL-3)-20 and (AL-3)-21, R^(L14) is as defined above. R^(L18) is a C₁-C₂₀ (h+1)-valent saturated hydrocarbylene group or C₆-C₂₀ (h+1)-valent arylene group, which may contain a heteroatom such as oxygen, sulfur or nitrogen. The saturated hydrocarbylene group may be straight, branched or cyclic. The subscript h is an integer of 1 to 3

Examples of the monomer from which repeat units containing an acid labile group of formula (AL-3) are derived include (meth)acrylates having an exo-form structure represented by the formula (AL-3)-22.

In formula (AL-3)-22, R^(A) is as defined above. R^(Lc1) is a C₁-C₈ saturated hydrocarbyl group or an optionally substituted C₆-C₂₀ aryl group; the saturated hydrocarbyl group may be straight, branched or cyclic. R^(Lc2) to R^(Lc11) are each independently hydrogen or a C₁-C₁₅ hydrocarbyl group which may contain a heteroatom; oxygen is a typical heteroatom. Suitable hydrocarbyl groups include C₁-C₁₅ alkyl groups and C₆-C₁₅ aryl groups. Alternatively, a pair of R^(Lc2) and R^(Lc3), R^(Lc4) and R^(Lc6), R^(Lc4) and R^(Lc7), R^(Lc5) and R^(Lc7), R^(Lc5) and R^(Lc11), R^(Lc6) and R^(Lc10), R^(Lc8) and R^(Lc9), or R^(Lc9) and R^(Lc10), taken together, may form a ring with the carbon atom to which they are attached, and in this event, the ring-forming group is a C₁-C₁₅ hydrocarbylene group which may contain a heteroatom. Also, a pair of R^(Lc2) and R^(Lc11), R^(Lc8) and R^(Lc11), or R^(Lc4) and R^(Lc6) which are attached to vicinal carbon atoms may bond together directly to form a double bond. The formula also represents an enantiomer.

Examples of the monomer having formula (AL-3)-22 are described in U.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limiting examples of suitable monomers are given below. R^(A) is as defined above.

Examples of the monomer from which the repeat units having an acid labile group of formula (AL-3) are derived include (meth)acrylates having a furandiyl, tetrahydrofurandiyl or oxanorbornanediyl group as represented by the following formula (AL-3)-23.

In formula (AL-3)-23, R^(A) is as defined above. R^(Lc12) and R^(Lc13) are each independently a C₁-C₁₀ hydrocarbyl group, or R^(Lc12) and R^(Lc13), taken together, may form an aliphatic ring with the carbon atom to which they are attached. R^(Lc14) is furandiyl, tetrahydrofurandiyl or oxanorbornanediyl. R^(Lc15) is hydrogen or a C₁-C₁₀ hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be straight, branched or cyclic, and is typically a C₁-C₁₀ saturated hydrocarbyl group.

Examples of the monomer having formula (AL-3)-23 are shown below, but not limited thereto. Herein R^(A) is as defined above.

The base polymer may further include repeat units (b) having an adhesive group. The adhesive group is selected from hydroxy, carboxy, lactone ring, carbonate bond, thiocarbonate bond, carbonyl, cyclic acetal, ether bond, ester bond, sulfonic ester bond, cyano, amide, —O—C(═O)—S— and —O—C(═O)—NH—.

Examples of the monomer from which repeat units (b) are derived are given below, but not limited thereto. Herein R^(A) is as defined above.

The base polymer may further include repeat units (c) of at least one type selected from repeat units having the following formulae (c1), (c2) and (c3). These units are simply referred to as repeat units (c1), (c2) and (c3), which may be used alone or in combination of two or more types.

In formulae (c1) to (c3), R^(A) is each independently hydrogen or methyl. Z¹ is a single bond, or a C₁-C₆ aliphatic hydrocarbylene group, phenylene group, naphthylene group, or a C₇-C₁₈ group obtained by combining the foregoing, or —O—Z¹¹—, —C(═O)—O—Z¹¹— or —C(═O)—NH—Z¹¹—, wherein Z¹¹ is a C₁-C₆ aliphatic hydrocarbylene group, phenylene group, naphthylene group, or a C₇-C₁₈ group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety. Z² is a single bond or ester bond. Z³ is a single bond, —Z³¹—C(═O)—O—, —Z³¹—O—, or —Z³¹—O—C(═O)—, wherein Z³¹ is a C₁-C₁₂ hydrocarbylene group, phenylene group or a C₇-C₁₈ group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, bromine or iodine. Z⁴ is methylene, 2,2,2-trifluoro-1,1-ethanediyl or carbonyl. Z⁵ is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene group, —O—Z⁵¹—, —C(═O)—O—Z⁵¹— or —C(═O)—NH—Z⁵¹—, wherein Z⁵¹ is a C₁-C₆ aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety.

In formulae (c1) to (c3), R³¹ to R³⁸ are each independently halogen or a C₁-C₂₀ hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C₁-C₂₀ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, heptadecyl, octadecyl, nonadecyl and icosyl; C₃-C₂₀ cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, adamantyl; C₂-C₂₀ alkenyl groups such as vinyl, propenyl, butenyl, hexenyl; C₃-C₂₀ unsaturated alicyclic hydrocarbyl groups such as cyclohexenyl and norbornenyl; C₂-C₂₀ alkynyl groups such as ethynyl, propynyl, butynyl; C₆-C₂₀ aryl groups such as phenyl, methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, sec-butylphenyl, tert-butylphenyl, naphthyl, methylnaphthyl, ethylnaphthyl, n-propylnaphthyl, isopropylnaphthyl, n-butylnaphthyl, isobutylnaphthyl, sec-butylnaphthyl, tert-butylnaphthyl; and C₇-C₂₀ aralkyl groups such as benzyl and phenethyl. In these groups, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or some carbon may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy moiety, halogen, cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonic ester bond, carbonate moiety, lactone ring, sultone ring, carboxylic anhydride or haloalkyl moiety.

Also, a pair of R³³ and R³⁴, or R³⁶ and R³⁷ may bond together to form a ring with the sulfur atom to which they are attached. Inter aha, rings of the following structure are preferred.

In formula (c1), M⁻ is a non-nucleophilic counter ion. Examples of the non-nucleophilic counter ion include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkyl sulfonate ions such as mesylate and butanesulfonate; imide ions such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide; methide ions such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide.

Also included are sulfonate ions having fluorine substituted at α-position as represented by the formula (c1-1) and sulfonate ions having fluorine substituted at α-position and trifluoromethyl at β-position as represented by the formula (c1-2).

In formula (c1-1), R⁴¹ is hydrogen, or a C₁-C₂₀ hydrocarbyl group which may contain an ether bond, ester bond, carbonyl moiety, lactone ring, or fluorine atom. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic and examples thereof are as exemplified above for the hydrocarbyl group R^(1a) in formula (1-1-1).

In formula (c1-2), R⁴² is hydrogen, or a C₁-C₃₀ hydrocarbyl group or C₂-C₃₀ hydrocarbylcarbonyl group which may contain an ether bond, ester bond, carbonyl moiety or lactone ring. The hydrocarbyl group and hydrocarbyl moiety in the hydrocarbylcarbonyl group may be saturated or unsaturated and straight, branched or cyclic and examples thereof are as exemplified above for the hydrocarbyl group R^(1a) in formula (1-1-1).

Examples of the cation in the monomer from which repeat unit (c1) is derived are shown below, but not limited thereto. R^(A) is as defined above.

Examples of the cation in the monomer from which repeat unit (c2) or (c3) is derived are shown below, but not limited thereto.

Examples of the anion in the monomer from which repeat unit (c2) is derived are shown below, but not limited thereto. R^(A) is as defined above.

Examples of the anion in the monomer from which repeat unit (c3) is derived are shown below, but not limited thereto. R^(A) is as defined above.

Besides the above-described repeat units, the base polymer may further include repeat units (d), which are derived from such monomers as styrene, acenaphthylene, indene, coumarin, and coumarone.

In the base polymer comprising repeat units (a1), (a2), (b), (c1), (c2), (c3), and (d), a fraction of these units is: preferably 0≤a1<1.0, 0≤a2<1.0, 0.1≤a1+a2<1.0, 0.1≤b≤0.9, 0≤c1≤0.6, 0≤c2≤0.6, 0≤c3≤0.6, 0≤c1+c2+c3≤0.6, and 0≤d≤0.5; more preferably 0≤a1≤0.8, 0≤a2≤0.8, 0.2≤a1+a2≤0.8, 0.2≤b≤0.8, 0≤c1≤0.5, 0≤c2≤0.5, 0≤c3≤0.5, 0≤c1+c2+c3≤0.5, and 0≤d≤0.4; and even more preferably 0≤a1≤0.7, 0≤a2≤0.7, 0.3≤a1+a2≤0.7, 0.25≤b≤0.7, 0≤c1≤0.4, 0≤c2≤0.4, 0≤c3≤0.4, 0≤c1+c2+c3≤0.4, and 0≤d≤0.3. Notably, a1+a2+b+c1+c2+c3+d=1.0.

The base polymer may be synthesized by any desired methods, for example, by dissolving suitable monomers selected from the monomers corresponding to the foregoing repeat units in an organic solvent, adding a radical polymerization initiator thereto, and heating for polymerization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran (THF), diethyl ether, and dioxane. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the reaction temperature is 50 to 80° C., and the reaction time is 2 to 100 hours, more preferably 5 to 20 hours.

In the case of a monomer having a hydroxy group, the hydroxy group may be replaced by an acetal group susceptible to deprotection with acid, typically ethoxyethoxy, prior to polymerization, and the polymerization be followed by deprotection with weak acid and water. Alternatively, the hydroxy group may be replaced by an acetyl, formyl, pivaloyl or similar group prior to polymerization, and the polymerization be followed by alkaline hydrolysis.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, an alternative method is possible. Specifically, acetoxystyrene or acetoxyvinylnaphthalene is used instead of hydroxystyrene or hydroxyvinylnaphthalene, and after polymerization, the acetoxy group is deprotected by alkaline hydrolysis, for thereby converting the polymer product to hydroxystyrene or hydroxyvinylnaphthalene. For alkaline hydrolysis, a base such as aqueous ammonia or triethylamine may be used. Preferably the reaction temperature is −20° C. to 100° C., more preferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours, more preferably 0.5 to 20 hours.

The base polymer should preferably have a weight average molecular weight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000 to 30,000, as measured by GPC versus polystyrene standards using tetrahydrofuran (THF) solvent. With too low a Mw, the resist composition may become less heat resistant. A polymer with too high a Mw may lose alkaline solubility and give rise to a footing phenomenon after pattern formation.

If a base polymer has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of Mw and Mw/Mn become stronger as the pattern rule becomes finer. Therefore, the base polymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

The base polymer may be a blend of two or more polymers which differ in compositional ratio, Mw or Mw/Mn.

(D) Organic Solvent

The positive resist composition may contain (D) an organic solvent. The organic solvent is not particularly limited as long as the foregoing components and other components are dissolvable therein. Examples of the organic solvent used herein are described in U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs [0144]-[0145]). Exemplary solvents include ketones such as cyclohexanone, cyclopentanone, methyl-2-n-pentyl ketone, and 2-heptanone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, l-methoxy-2-propanol, 1-ethoxy-2-propanol, and diacetone alcohol (DAA); ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; and lactones such as γ-butyrolactone, and mixtures thereof.

The organic solvent is preferably added in an amount of 100 to 10,000 parts, and more preferably 200 to 8,000 parts by weight per 100 parts by weight of the base polymer (C).

(E) Surfactant

The resist composition may further comprise (E) a surfactant. Exemplary surfactants are described in JP-A 2008-111103, paragraphs [0165]-[0166], Inclusion of a surfactant may improve or control the coating characteristics of the resist composition. When used, the surfactant is preferably added in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the base polymer (C). The surfactant may be used alone or in admixture.

(F) Other Acid Generator

The resist composition may further comprise (F) an acid generator other than component (A) (referred to as other acid generator, hereinafter). The acid generator is capable of generating a strong acid. As used herein, the term “strong acid” refers to a compound having a sufficient acidity to induce deprotection reaction of an acid labile group on the base polymer. The acid generator is typically a compound (PAG) capable of generating an acid upon exposure to actinic ray or radiation. Although the PAG used herein may be any compound capable of generating an acid upon exposure to high-energy radiation, those compounds capable of generating sulfonic acid, imide acid (imidic acid) or methide acid are preferred. Suitable PAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. Exemplary PAGs are described in JP-A 2008-111103, paragraphs [0122]-[0142] (U.S. Pat. No. 7,537,880).

Also included in the other acid generator are sulfonium salts having the formula (1-1) (exclusive of those salts containing fluorine in both anion and cation), iodonium salts having the formula (1-2), betaine type sulfonium compounds having the formula (2), and sulfonium salts having the formula (3-1) (exclusive of those salts containing fluorine in both anion and cation), and iodonium salts having the formula (3-2), as described in JP-A 2020-122956.

In the resist composition containing the other acid generator (F), its content is preferably 0.1 to 30 parts by weight, and more preferably 0.2 to 20 parts by weight per 100 parts by weight of the base polymer (C) although the content is not particularly limited as long as the benefits of the invention are not impaired.

(G) Other Quencher

The resist composition may further comprise (G) a quencher other than component (B) (referred to as other quencher, hereinafter).

The other quencher is typically selected from conventional basic compounds. Conventional basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, nitrogen-containing compounds with carboxy group, nitrogen-containing compounds with sulfonyl group, nitrogen-containing compounds with hydroxy group, nitrogen-containing compounds with hydroxyphenyl group, alcoholic nitrogen-containing compounds, amide derivatives, imide derivatives, and carbamate derivatives. Also included are primary, secondary, and tertiary amine compounds, specifically amine compounds having a hydroxy group, ether bond, ester bond, lactone ring, cyano group, or sulfonic acid ester bond as described in JP-A 2008-111103, paragraphs [0146]-[0164], and compounds having a carbamate group as described in JP 3790649. Addition of such a basic compound is effective for further suppressing the diffusion rate of acid in the resist film or correcting the pattern profile.

Onium salts such as sulfonium salts, iodonium salts and ammonium salts of sulfonic acids which are not fluorinated at α-position as described in U.S. Pat. No. 8,795,942 (JP-A 2008-158339) and similar onium salts of carboxylic acid may also be used as the other quencher. While an α-fluorinated sulfonic acid, imide acid, and methide acid are necessary to deprotect the acid labile group of carboxylic acid ester, an α-non-fluorinated sulfonic acid or carboxylic acid are released by salt exchange with an α-non-fluorinated onium salt. An α-non-fluorinated sulfonic acid or carboxylic acid function as a quencher because they do not induce deprotection reaction.

Suitable other quenchers include sulfonium salts having an iodized phenyl group (exclusive of those salts containing fluorine in both anion and cation) as described in JP-A 2017-219836. Since iodine is highly absorptive to EUV of wavelength 13.5 nm, it generates secondary electrons upon EUV exposure. The energy of secondary electrons is transferred to the acid generator to promote its decomposition, contributing to a higher sensitivity.

Also useful are quenchers of polymer type as described in U.S. Pat. No. 7,598,016 (JP-A 2008-239918). The polymeric quencher segregates at the resist film surface and thus enhances the rectangularity of resist pattern. When a protective film is applied as is often the case in the immersion lithography, the polymeric quencher is also effective for preventing a film thickness loss of resist pattern or rounding of pattern top.

The other quencher (G) is preferably added in an amount of 0.001 to 20 parts, more preferably 0.01 to 10 parts by weight per 100 parts by weight of the base polymer (C) although the content is not particularly limited as long as the benefits of the invention are not impaired. The other quencher may be used alone or in admixture.

Other Components

With the foregoing components, the resist composition may further include other components such as a dissolution inhibitor, water repellency improver, and acetylene alcohol.

The inclusion of a dissolution inhibitor may lead to an increased difference in dissolution rate between exposed and unexposed areas and a further improvement in resolution. The dissolution inhibitor which can be used herein is a compound having at least two phenolic hydroxy groups on the molecule, in which an average of from 0 to 100 mol % of all the hydrogen atoms on the phenolic hydroxy groups are replaced by acid labile groups or a compound having at least one carboxy group on the molecule, in which an average of 50 to 100 mol % of all the hydrogen atoms on the carboxy groups are replaced by acid labile groups, both the compounds having a molecular weight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenol A, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylic acid, adamantanecarboxylic acid, and cholic acid derivatives in which the hydrogen atom on the hydroxy or carboxy group is replaced by an acid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A 2008-122932, paragraphs [0155]-[0178]).

In the resist composition, the dissolution inhibitor is preferably added in an amount of 0 to 50 parts, more preferably 5 to 40 parts by weight per 100 parts by weight of the base polymer (C). The dissolution inhibitor may be used alone or in admixture.

The water repellency improver is added for improving the water repellency on surface of a resist film. The water repellency improver may be used in the topcoatless immersion lithography. Suitable water repellency improvers include polymers having a fluoroalkyl group and polymers having a specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A 2007-297590 and JP-A 2008-111103, for example. The water repellency improver to be added to the resist composition should be soluble in the alkaline developer and organic solvent developer. The water repellency improver of specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue is well soluble in the developer. A polymer having an amino group or amine salt copolymerized as repeat units may serve as the water repellent additive and is effective for preventing evaporation of acid during PEB, thus preventing any hole pattern opening failure after development. An appropriate amount of the water repellency improver is 0 to 20 parts, more preferably 0.5 to 10 parts by weight per 100 parts by weight of the base polymer (C). The water repellency improver may be used alone or in admixture.

Suitable acetylene alcohols are described in JP-A 2008-122932, paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcohol blended is 0 to 5 parts by weight per 100 parts by weight of the base polymer (C). The acetylene alcohol may be used alone or in admixture.

Pattern Forming Process

The positive resist composition is used in the fabrication of various integrated circuits. Pattern formation using the resist composition may be performed by well-known lithography processes. The process generally involves the steps of applying the resist composition to form a resist film on a substrate, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer. If necessary, any additional steps may be added.

Specifically, the positive resist composition is first applied onto a substrate on which an integrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO, CrON, MoSi₂, or SiO₂) by a suitable coating technique such as spin coating, roll coating, flow coating, dipping, spraying or doctor coating. The coating is prebaked on a hot plate at a temperature of 60 to 150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C. for 30 seconds to 20 minutes. The resulting resist film is generally 0.01 to 2 μm thick.

The resist film is then exposed to a desired pattern of high-energy radiation such as UV, deep-UV, EB, EUV of wavelength 3 to 15 nm, x-ray, soft x-ray, excimer laser light, γ-ray or synchrotron radiation. When UV, deep-UV, EUV, x-ray, soft x-ray, excimer laser light, γ-ray or synchrotron radiation is used as the high-energy radiation, the resist film is exposed thereto directly or through a mask having a desired pattern in a dose of preferably about 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm². When EB is used as the high-energy radiation, the resist film is exposed thereto directly or through a mask having a desired pattern in a dose of preferably about 0.1 to 100 μC/cm², more preferably about 0.5 to 50 μC/cm². It is appreciated that the inventive resist composition is suited in micropatterning using i-line of wavelength 365 nm, KrF excimer laser, ArF excimer laser, EB, EUV, x-ray, soft x-ray, γ-ray or synchrotron radiation, especially in micropatterning using EB or EUV.

After the exposure, the resist film may be baked (PEB) on a hot plate or in an oven at 50 to 150° C. for 10 seconds to 30 minutes, preferably at 60 to 120° C. for 30 seconds to 20 minutes.

After the exposure or PEB, the resist film is developed in a developer in the form of an aqueous base solution for 3 seconds to 3 minutes, preferably 5 seconds to 2 minutes by conventional techniques such as dip, puddle and spray techniques. A typical developer is a 0.1 to 10 wt %, preferably 2 to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), or tetrabutylammonium hydroxide (TBAH). The resist film in the exposed area is dissolved in the developer whereas the resist film in the unexposed area is not dissolved. In this way, the desired positive pattern is formed on the substrate.

In an alternative embodiment, a negative pattern may be formed from the positive resist composition via organic solvent development. The developer used herein is preferably selected from among 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, butyl formate, isobutyl formate, pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate, pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzyl formate, phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsing liquid, a solvent which is miscible with the developer and does not dissolve the resist film is preferred. Suitable solvents include alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, and aromatic solvents. Specifically, suitable alcohols of 3 to 10 carbon atoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, tert-pentyl alcohol, neopentyl alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol, cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbon atoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether, di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-pentyl ether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atoms include hexane, heptane, octane, nonane, decane, undecane, dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, and cyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene, heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene, cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atoms include hexyne, heptyne, and octyne. Suitable aromatic solvents include toluene, xylene, ethylbenzene, isopropylbenzene, tert-butylbenzene and mesitylene. The solvents may be used alone or in admixture.

Rinsing is effective for minimizing the risks of resist pattern collapse and defect formation. However, rinsing is not essential. If rinsing is omitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermal flow, RELACS® or DSA process. A hole pattern is shrunk by coating a shrink agent thereto, and baking such that the shrink agent may undergo crosslinking at the resist surface as a result of the acid catalyst diffusing from the resist layer during bake, and the shrink agent may attach to the sidewall of the hole pattern. The bake is preferably at a temperature of 70 to 180° C., more preferably 80 to 170° C., for a time of 10 to 300 seconds. The extra shrink agent is stripped and the hole pattern is shrunk.

EXAMPLES

Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviation “pbw” is parts by weight.

Synthesis Examples 1-1 to 1-5

Synthesis of Base Polymers P-1 to P-5

Each of base polymers P-1 to P-5 was prepared by combining suitable monomers, effecting copolymerization reaction thereof in tetrahydrofuran (THF) solvent, pouring the reaction solution into methanol for crystallization, washing the precipitate with hexane, isolation, and drying. The resulting polymer was analyzed for composition by ¹H-NMR spectroscopy, and for Mw and Mw/Mn by GPC versus polystyrene standards using THF solvent.

Synthesis Example 2-1

Synthesis of Acid Generator PAG-1

(1) Synthesis of Intermediate In-1

In 1,050 g of dichloromethane were dissolved 150 g of Compound C-1 and 87.6 of Compound C-2 which was synthesized according to the method described in JP-A 2016-218089 or US 20160334706. Under ice cooling, a solution of 32.7 g of triethylamine (TEA) and 2.8 g of N,N-dimethyl-4-aminopyridine (DMAP) in 100 g of dichloromethane was added to the above solution. After stirring was continued at room temperature for 1 hour, 300 g of a 10 wt % aqueous solution of sodium hydrogencarbonate was added to the solution, which was stirred at room temperature for 20 minutes. An organic layer was taken out, washed with deionized water, and concentrated under reduced pressure. To the residue was added 600 g of hexane. The thus precipitated crystal was recovered by filtration and dried in vacuum. There was obtained the end compound, Intermediate In-1 (amount 187 g, yield 94%). The results of ¹H-NMR analysis are shown below.

¹H-NMR (500 MHz, DMSO-d6): δ=3.00 (9H, s), 4.50 (2H, s), 6.18 (1H, m), 7.52 (5H, s), 8.03 (1H, s), 8.44 (1H, s) ppm

(2) Synthesis of Acid Generator PAG-1

In a mixture of 84.7 g of methyl isobutyl ketone (MIBK) and 5 g of methanol, 17.2 g of In-1 and 8.74 g of Compound C-3 were dissolved. The solution was stirred at room temperature for 30 minutes. An organic layer was taken out, washed with deionized water, and concentrated under reduced pressure. To the residue was added 70 g of hexane. The thus precipitated crystal was recovered by filtration and dried in vacuum. There was obtained the target compound, PAG-1 (amount 17.5 g, yield 84%). The results of ¹H- and ¹⁹F-NMR analyses are shown below.

¹H-NMR (500 MHz, DMSO-d6): δ=6.17 (1H, m), 7.63-7.68 (6H, m), 7.90-7.94 (6H, m), 8.03 (1H, s), 8.44 (1H, s) ppm

¹⁹F-NMR (500 MHz, DMSO-d6): δ=−121 (1F, m), −113 (1F, m), −105 (3F, s), −71.3 (3F, m) ppm

Synthesis Examples 2-2 to 2-22

Synthesis of Acid Generators PAG-2 to PAG-22

Acid generators PAG-2 to PAG-22 were synthesized with reference to Synthesis Example 2-1. Their structure is shown below.

Examples 1 to 42 and Comparative Examples 1 to 6

Preparation and Evaluation of Positive Resist Compositions

(1) Preparation of Positive Resist Composition

Positive resist compositions were prepared by dissolving components in an organic solvent containing 50 ppm of surfactant Polyfox 636 (Omnova Solutions Inc.) in accordance with the formulation shown in Tables 1 to 4, and filtering through a filter with a pore size of 0.2 μm.

The components in Tables 1 to 4 are identified below.

Organic Solvent:

PGMEA=propylene glycol monomethyl ether acetate

DAA=diacetone alcohol

Comparative Acid Generators (cPAG-1, cPAG-2):

Quenchers: Q-1 to Q-26

Comparative Quenchers: cQ-1 to cQ-5

(2) Evaluation by EUV Lithography

Each of the resist compositions in Tables 1 to 4 was spin coated on a silicon substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., Si content 43 wt %) and prebaked on a hotplate at 105° C. for 60 seconds to form a resist film of 60 nm thick. Using an EUV scanner NXE3400 (ASML, NA 0.33, σ 0.9/0.6, quadrupole illumination), the resist film was exposed to EUV through a mask bearing a hole pattern at a pitch 46 nm (on-wafer size) and +20% bias. The resist film was baked (PEB) on a hotplate at the temperature shown in Tables 1 to 4 for 60 seconds and developed in a 2.38 wt % TMAH aqueous solution for 30 seconds to form a hole pattern having a size of 23 nm.

The resist pattern was observed under CD-SEM (CG5000, Hitachi High-Technologies Corp.). The exposure dose that provides a hole pattern having a size of 23 nm is reported as sensitivity. The size of 50 holes was measured, from which a 3-fold value (3σ) of standard deviation (σ) was computed and reported as size variation or CDU.

The resist composition is shown in Tables 1 to 4 together with the sensitivity and CDU of EUV lithography.

TABLE 1 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 1 P-1 PAG-1 Q-1 PGMEA (2,000) 80 29 2.6 (100) (30.3) (4.86) DAA (500) 2 P-1 PAG-1 Q-2 PGMEA (2,000) 80 27 2.6 (100) (30.3) (5.07) DAA (500) 3 P-1 PAG-1 Q-3 PGMEA (2,000) 80 28 2.6 (100) (30.3) (5.55) DAA (500) 4 P-1 PAG-1 Q-4 PGMEA (2,000) 80 26 2.4 (100) (30.3) (5.28) DAA (500) 5 P-1 PAG-1 Q-5 PGMEA (2,000) 80 30 2.5 (100) (30.3) (4.76) DAA (500) 6 P-1 PAG-1 Q-6 PGMEA (2,000) 80 29 2.4 (100) (30.3) (5.42) DAA (500) 7 P-1 PAG-1 Q-7 (2.42) PGMEA (2,000) 80 28 2.5 (100) (30.3) Q-8 (2.52) DAA (500) 8 P-1 PAG-1 Q-9 PGMEA (2,000) 80 29 2.4 (100) (30.3) (6.20) DAA (500) 9 P-1 PAG-1 Q-10 PGMEA (2,000) 80 28 2.5 (100) (30.3) (4.63) DAA (500) 10 P-1 PAG-1 Q-11 PGMEA (2,000) 80 30 2.4 (100) (30.3) (7.14) DAA (500) 11 P-1 PAG-1 Q-12 PGMEA (2,000) 80 29 2.4 (100) (30.3) (6.72) DAA (500) 12 P-1 PAG-1 Q-13 PGMEA (2,000) 80 29 2.3 (100) (30.3) (6.16) DAA (500) 13 P-1 PAG-2 Q-4 PGMEA (2,000) 80 28 2.4 (100) (29.2) (5.28) DAA (500) 14 P-1 PAG-3 Q-4 PGMEA (2,000) 80 27 2.4 (100) (29.8) (5.28) DAA (500) 15 P-1 PAG-4 Q-4 PGMEA (2,000) 80 26 2.4 (100) (30.8) (5.28) DAA (500) 16 P-1 PAG-5 Q-4 PGMEA (2,000) 80 29 2.4 (100) (34.3) (5.28) DAA (500) 17 P-1 PAG-6 Q-4 PGMEA (2,000) 80 28 2.2 (100) (34.2) (5.28) DAA (500) 18 P-1 PAG-7 Q-4 PGMEA (2,000) 80 28 2.4 (100) (27.5) (5.28) DAA (500) 19 P-1 PAG-8 Q-4 PGMEA (2,000) 80 28 2.5 (100) (28.1) (5.28) DAA (500) 20 P-1 PAG-9 Q-4 PGMEA (2,000) 80 29 2.3 (100) (28.4) (5.28) DAA (500)

TABLE 2 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 21 P-1 PAG-10 Q-4 PGMEA (2,000) 80 27 2.4 (100) (27.7) (5.28) DAA (500) 22 P-2 PAG-11 Q-4 PGMEA (2,000) 85 29 2.4 (100) (10.2) (5.28) DAA (500) 23 P-3 PAG-12 Q-4 PGMEA (2,000) 85 26 2.2 (100) (9.1) (5.28) DAA (500) 24 P-4 PAG-13 Q-4 PGMEA (2,000) 85 25 2.4 (100) (11.2) (5.28) DAA (500) 25 P-5 PAG-14 Q-4 PGMEA (2,000) 85 37 2.3 (100) (11.3) (5.28) DAA (500) 26 P-5 PAG-15 Q-4 PGMEA (2,000) 85 28 2.1 (100) (11.7) (5.28) DAA (500) 27 P-5 PAG-16 Q-4 PGMEA (2,000) 85 31 2.6 (100) (9.3) (5.28) DAA (500) 28 P-5 PAG-17 Q-14 PGMEA (2,000) 80 31 2.5 (100) (8.2) (3.94) DAA (500) 29 P-5 PAG-18 Q-15 PGMEA (2,000) 80 34 2.2 (100) (8.2) (3.76) DAA (500)

TABLE 3 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 30 P-5 PAG-18 Q-16 PGMEA (2,000) 80 26 2.6 (100) (8.2) (6.70) DAA (500) 31 P-5 PAG-19 Q-17 PGMEA (2,000) 80 33 2.4 (100) (12.0) (4.54) DAA (500) 32 P-5 PAG-20 Q-18 PGMEA (2,000) 80 32 2.4 (100) (12.4) (4.72) DAA (500) 33 P-5 PAG-20 Q-19 PGMEA (2,000) 80 27 2.3 (100) (12.4) (4.98) DAA (500) 34 P-5 PAG-20 Q-20 PGMEA (2,000) 80 24 2.6 (100) (12.4) (5.48) DAA (500) 35 P-5 PAG-20 Q-21 PGMEA (2,000) 80 27 2.3 (100) (12.4) (4.46) DAA (500) 36 P-5 PAG-20 Q-22 PGMEA (2,000) 80 22 2.6 (100) (12.4) (6.00) DAA (500) 37 P-5 PAG-20 Q-23 PGMEA (2,000) 80 26 2.2 (100) (12.4) (6.13) DAA (500) 38 P-5 PAG-20 Q-24 PGMEA (2,000) 80 27 2.2 (100) (12.4) (5.23) DAA (500) 39 P-5 PAG-20 Q-25 PGMEA (2,000) 80 26 2.3 (100) (12.4) (5.50) DAA (500) 40 P-1 PAG-20 Q-26 PGMEA (2,000) 80 26 2.4 (100) (31.0) (5.46) DAA (500) 41 P-1 PAG-21 Q-26 PGMEA (2,000) 80 29 2.3 (100) (29.2) (5.46) DAA (500) 42 P-1 PAG-22 Q26 PGMEA (2,000) 80 30 2.2 (100) (30.2) (5.46) DAA (500) Compar- 1 P-1 cPAG-1 Q-1 PGMEA (2,000) 80 35 3.0 ative (100) (24.2) (4.86) DAA (500) Example 2 P-1 cPAG-1 Q-1 PGMEA (2,000) 80 33 2.8 (100) (29.8) (4.02) DAA (500) 3 P-1 cPAG-2 Q-2 PGMEA (2,000) 80 30 3.4 (100) (24.2) (4.02) DAA (500) 4 P-1 cPAG-1 Q-3 PGMEA (2,000) 80 33 2.8 (100) (29.8) (4.02) DAA (500) 5 P-1 cPAG-1 Q-4 PGMEA (2,000) 80 32 2.8 (100) (29.8) (4.20) DAA (500) 6 P-1 cPAG-1 Q-5 PGMEA (2,000) 80 30 2.8 (100) (29.8) (4.7) DAA (500)

TABLE 4 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Compar- 1 P-1 cPAG-1 Q-1 PGMEA (2,000) 80 35 3.0 ative (100) (24.2) (4.86) DAA (500) Example 2 P-1 cPAG-1 cQ-1 PGMEA (2,000) 80 33 2.8 (100) (29.8) (4.02) DAA (500) 3 P-1 cPAG-2 cQ-2 PGMEA (2,000) 80 30 3.4 (100) (24.2) (4.02) DAA (500) 4 P-1 PAG-1 cQ-3 PGMEA (2,000) 80 33 2.8 (100) (29.8) (4.02) DAA (500) 5 P-1 PAG-1 cQ-4 PGMEA (2,000) 80 32 2.8 (100) (29.8) (4.20) DAA (500) 6 P-1 PAG-1 cQ-5 PGMEA (2,000) 80 30 2.8 (100) (29.8) (4.7) DAA (500)

It is evident from Tables 1 to 4 that the positive resist compositions comprising an acid generator in the form of a sulfonium salt consisting of a fluorine-containing sulfonate anion and a fluorine-containing sulfonium cation and a quencher in the form of a sulfonium salt containing at least two fluorine atoms in its cation or containing at least 5 fluorine atoms in its anion and cation exhibit a high sensitivity and improved CDU.

Japanese Patent Application No. 2020-166646 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A positive resist composition comprising: (A) an acid generator in the form of a sulfonium salt consisting of a sulfonate anion having at least one fluorine atom and a sulfonium cation having at least one fluorine atom, (B) a quencher in the form of a sulfonium salt consisting of a cation and an anion, the cation containing at least two fluorine atoms or the anion and cation containing at least 5 fluorine atoms in total, and (C) a base polymer comprising repeat units of at least one type selected from repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group.
 2. The resist composition of claim 1 wherein the quencher (B) is a sulfonium salt in which the cation contains at least 3 fluorine atoms or the anion and cation contain at least 6 fluorine atoms in total.
 3. The resist composition of claim 1 wherein the sulfonate anion in the acid generator (A) further contains an iodine atom.
 4. The resist composition of claim 1 wherein the sulfonate anion in the acid generator (A) has the formula (1-1) or (1-2):

wherein R¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine, and R² is a C₁-C₄₀ hydrocarbyl group which may contain a heteroatom exclusive of iodine.
 5. The resist composition of claim 3 wherein the sulfonate anion has the formula (1-3):

wherein p is an integer of 1 to 3, q is an integer of 1 to 5, r is an integer of 0 to 3, and q+r is from 1 to 5, L¹ is a single bond, ether bond, ester bond, amide bond, imide bond or a C₁-C₆ saturated hydrocarbylene group in which any constituent —CH₂— may be replaced by an ether bond or ester bond, L² is a single bond or C₁-C₂₀ hydrocarbylene group which may contain a heteroatom in case of p=1, and a C₁-C₂₀ (p+1)-valent hydrocarbon group which may contain a heteroatom in case of p=2 or 3, L³ is a single bond, ether bond or ester bond, Rf¹ to Rf⁴ are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf¹ to Rf⁴ being fluorine or trifluoromethyl, and Rf¹ and Rf², taken together, may form a carbonyl group, R³ is a hydroxy group, carboxy group, fluorine, chlorine, bromine, or amino group, or a C₁-C₂₀ hydrocarbyl group, C₁-C₂₀ hydrocarbyloxy group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbyloxycarbonyl group, C₂-C₂₀ hydrocarbylcarbonyloxy group, or C₁-C₂₀ hydrocarbylsulfonyloxy group, which may contain fluorine, chlorine, bromine, hydroxy, amino or ether bond, or —N(R^(3A))(R^(3B)), —N(R^(3C))—C(═O)—R^(3D) or —N(R^(3C))—C(═O)—O—R^(3D), wherein R^(3A) and R^(3B) are each independently hydrogen or a C₁-C₆ saturated hydrocarbyl group, R^(3C) is hydrogen or a C₁-C₆ saturated hydrocarbyl group, in which some or all hydrogen may be substituted by a halogen, hydroxy moiety, C₁-C₆ saturated hydrocarbyloxy moiety, C₂-C₆ saturated hydrocarbylcarbonyl moiety, or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety, and R^(3D) is a C₁-C₁₆ aliphatic hydrocarbyl group, C₆-C₁₂ aryl group or C₇-C₁₅ aralkyl group, in which some or all hydrogen may be substituted by a halogen, hydroxy moiety, C₁-C₆ saturated hydrocarbyloxy moiety, C₂-C₆ saturated hydrocarbylcarbonyl moiety, or C₂-C₆ saturated hydrocarbylcarbonyloxy moiety.
 6. The resist composition of claim 1 wherein the anion of the sulfonium salt as quencher (B) is a carboxylate, sulfonamide, alkoxide or non-α-fluorinated sulfonate anion.
 7. The resist composition of claim 6 wherein the carboxylate anion has the formula (2-1), the sulfonamide anion has the formula (2-2), the alkoxide anion has the formula (2-3), and the non-α-fluorinated sulfonate anion has the formula (2-4):

wherein R¹¹ is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine or a heteroatom exclusive of fluorine, R¹² is fluorine or a C₁-C₄₀ hydrocarbyl group which may contain fluorine or a heteroatom exclusive of fluorine, R¹³ is hydrogen or a C₁-C₂₀ hydrocarbyl group which may contain a heteroatom, R¹⁴ is a C₁-C₈ saturated hydrocarbyl group having at least two fluorine atoms or a C₆-C₁₀ aryl group having at least two fluorine atoms, R¹⁵ is a C₁-C₁₂ aliphatic hydrocarbyl group or C₆-C₁₀ aryl group, any constituent —CH₂— in the aliphatic hydrocarbyl group may be replaced by —N(H)—, ether bond, or ester bond, some or all of the hydrogen atoms in the aliphatic hydrocarbyl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₆-C₁₀ aryl moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, some or all of the hydrogen atoms in the aryl group may be substituted by a halogen atom, hydroxy moiety, carboxy moiety, C₁-C₁₂ hydrocarbyloxy moiety, C₂-C₁₂ hydrocarbylcarbonyl moiety, or C₁-C₁₂ hydrocarbylcarbonyloxy moiety, with the proviso that R¹⁵ has no fluorine at the α-position relative to the sulfo group.
 8. The resist composition of claim 1 wherein in the sulfonium salt (A), the sulfonium cation having at least one fluorine atom has the formula (3):

wherein R^(a1) is a C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one atom selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine, R^(a2) and R^(a3) are each independently a C₁-C₂₀ hydrocarbyl group or C₁-C₂₀ hydrocarbyl group substituted with at least one fluorine, which may contain at least one atom selected from oxygen, sulfur, nitrogen, and halogen exclusive of fluorine, R^(a1) and R^(a2), or R^(a2) and R^(a3) may bond together to form a ring with the sulfur atom to which they are attached.
 9. The resist composition of claim 1 wherein the repeat unit (a1) has the formula (a1) and the repeat unit (a2) has the formula (a2):

wherein R^(A) is each independently hydrogen or methyl, X¹ is a single bond, phenylene group, naphthylene group, or a C₁-C₁₂ linking group containing at least one moiety selected from an ether bond, ester bond and lactone ring, X² is a single bond, ester bond or amide bond, X³ is a single bond, ether bond or ester bond, R²¹ and R²² are each independently an acid labile group, R²³ is fluorine, trifluoromethyl, cyano or a C₁-C₆ saturated hydrocarbyl group, R²⁴ is a single bond or a C₁-C₆ alkanediyl group in which some carbon may be replaced by an ether bond or ester bond, a is 1 or 2, b is an integer of 0 to 4, and 1≤a+b≤5.
 10. The resist composition of claim 1 wherein the base polymer further comprises repeat units containing an adhesive group selected from among hydroxy, carboxy, lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether bond, ester bond, sulfonic ester bond, cyano, amide bond, —O—C(═O)—S—, and —O—C(═O)—NH—.
 11. The resist composition of claim 1, further comprising (D) an organic solvent.
 12. The resist composition of claim 1, further comprising (E) a surfactant.
 13. A pattern forming process comprising the steps of applying the positive resist composition of claim 1 to form a resist film on a substrate, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer.
 14. The pattern forming process of claim 13 wherein the high-energy radiation is i-line, KrF excimer laser, ArF excimer laser, EB, or EUV of wavelength 3 to 15 nm.
 15. A sulfonium salt having the formula (1-3-1):

wherein R⁴ is a single bond or C₁-C₆ alkanediyl group, R⁵ is hydrogen or trifluoromethyl, and X is hydroxy or iodine. 